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Udaykumar Batchu Advisor: Dr. Clinton Jeffery. An Improved C Calling Interface for Unicon Language. A Brief Introduction to the Unicon Language. Is a high level programming language Derives Its name from Icon, originated from University of Arizona

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Udaykumar batchu advisor dr clinton jeffery

Udaykumar Batchu

Advisor: Dr. Clinton Jeffery

An Improved C Calling Interface for Unicon Language

A brief introduction to the unicon language
A Brief Introduction to the Unicon Language

  • Is a high level programming language

  • Derives Its name from Icon, originated from University of Arizona

  • Offers support for various data types, structures, procedures, high-level graphics functions and object oriented facilities

  • Easy for application development involving objects, networks and databases and simpler syntax than C and many other high level languages

  • Is highly portable

Basic data types of unicon
Basic Data Types of Unicon

All the basic data types are Immutable

  • Integers: size of long int; are of arbitrary precision

  • Real: double-precision floating point values

  • String: similar to C; includes escape sequences and special characters

  • Cset: character sets represented within single quotes

Unicon structures
Unicon Structures

Unicon provides four different types of structures. All can hold heterogeneous values

  • Lists: useful for representing arrays, queues, linked lists and stacks; declared with list() function

  • Tables: similar to associative arrays; declared with table() function

  • Records: similar C structures; declared with record() function

  • Sets: used for holding unordered collection of values; declared with set() function

  • Classes: similar to classes found in C++

String scanning in unicon
String Scanning in Unicon

str ? expression

  • str is the subject string used for string scanning operations

  • expression is/are the set of operations to be performed on str

  • nested string scanning expressions are possible

  • can design flexible and readable string scanning expressions

  • easier regular expressions and pattern matching actions

  • Unicon provides a variety functions for use with string scanning


    str ? {

    while tab(upto(&letters))do



    writes out all the set of words found in the string str

Procedures in unicon
Procedures in Unicon

  • Procedures in Unicon are declared with the keyword procedure

  • procedure main()is the start of any Unicon program

  • All parameters are passed by value except for structures

  • parameter types are not declared; they are intuitive

    e.g. sample Unicon procedure

    procedure array(i, j, x)

    local L

    L := list(i)

    every !L := list(j, x)

    return L


Introduction to the problem
Introduction to the Problem

Goal: Using the existing code written in C language, inside Unicon Programs

Earlier Mechanism:

  • Support was available only for few data types

  • Manual Updating of Makefile and shared library

  • Wrapper code need to be hand written

  • Building and linking the shared library for calling C functions


  • Automate the whole process mentioned above

  • Make it easier to call external C functions inside Unicon programs

  • Earlier mechanism
    Earlier Mechanism

    • C functions were called with

      • pathload (filename, funcname)

        filename – shared library name containing the C function

        funcname – name of the C function

    • pathload uses loadfunc which in turn uses dynamic loading and loads the external C function dynamically at runtime

    • Making entries into the Makefile; building it for Shared library creation or updating the existing one

    Earlier mechanism contd
    Earlier Mechanism contd…

    Supplying files to Makefile:

    FUNCS = bitcount.o files.o fpoll.o internal.o lgconv.o osf.o \

    pack.o ppm.o process.o tconnect.o fibonacci.o

    CSRC = bitcount.c files.c fpoll.c internal.c lgconv.c osf.c \ pack.c ppm.c process.c tconnect.c fibonacci.c

    FUNCS: Object files CSRC: C language Source files

    • UNIX Shell scripts were used for building the shared library and Icon/Unicon stubs

    Earlier mechanism steps followed
    Earlier Mechanism - Steps followed

    • Write or locate the C code to be called

    • For the C function(s) to be called, the programmer needs to write wrapper code using macros present in “icall.h” header file

    • Build (Update) the shared library with an entry for the new C function

    • Write a Unicon/Icon stub procedure to call the wrapper function: which is used for data type conversions

    • Link the external C function inside the Unicon program

    Steps to be Followed

    Step 1)Example: C code for Fibonacci Series using recursion: fibonacci.c

    int fibonacci(int n)


    if(n<2)return 1;


    return (fibonacci(n-1) + fibonacci(n-2));


    Step 2) Wrapper Code for Fibonacci: fibonacciwrap.c

    int fibonacciwrap(int argc, descriptor *argv)


    unsigned long v;

    int n;

    ArgInteger(1); /* validate type */

    v = IntegerVal(argv[1]); /* convert to C type */

    n = fibonacci(v);

    RetInteger(n); /* return the value to Unicon */


    Steps to be followed contd
    Steps to be Followed - contd…

    Step 3) Building the Shared Library

    • Compile the above two files and update the makefile to create a shared called “libcfunc.so”

      Step 4) Creation of Icon/Unicon Stub:

      procedure fibonacci(a[]) #:Fibonacci

      if fibonacci := pathload("libcfunc.so", "fibonacciwrap") then

      return fibonacci(n)


    • The above entry is created in “cfunc.icn” under /unicon/ipl/cfuncs/ during the updation of shared library

      Step 5) Linking the external C Program

    • Adding the statement ‘link cfunc’ inside the Unicon program for calling the external C function

    Calling c function from unicon
    Calling C function from Unicon

    Example Unicon Program: “foo.icn” using “fibonacci” from C function

    link cfunc

    procedure main()

    local i

    write("Enter value for fibonacci")

    i := read()

    write("Value of Fibonacci is:", fibonacci(i) )


    • “libcfunc.so” is the shared library file, where we can find the C function ‘fibonacci’ to be loaded dynamically at runtime using loadfunc

    Improved mechanism overview
    Improved Mechanism - Overview

    New Preprocessor Directives and more

    • “$libc” and “$libcend” preprocessor directives within which external C functions can be declared

    • Providing room for function signatures for the external C functions being used in Unicon with these new preprocessor directives

    • External C function signatures are grabbed as a string and processed within the preprocessor

    Improved mechanism contd
    Improved Mechanism contd…

    • Automatic wrapper code generation along with Icon/Unicon stubs takes place during preprocessing stage of compilation

    • Unicon translator also builds the Shared library for loading the external C functions used inside the Unicon program

    • Each Unicon (*.icn) program has its own shared library built when C functions are used in it.

    • Support is provided for basic data types such as: Integers, Real’s and Characters along with Integer and Real Arrays

    Implementation changes to the unicon language
    Implementation: Changes to the Unicon Language

    Unicon Source Program

    Unicon Preprocessor




    Automatic Wrapper Code generation

    Building the shared library

    Generation of Icon/Unicon stubs

    • Preprocessor code is modified at /unicon/uni/preproce.icn

    • Macros used for handling arrays are tweaked at /unicon/src/runtime/rstruct.r

    • All the work is developed under 32-bit Linux (Kernel Version environment and is easily portable to other platforms

    • Existing Macros for handling Integers, Reals and Strings are used

    Improved mechanism example
    Improved Mechanism – example

    Beginning place for external C code

    procedure main()

    local a, b

    a :=4

    b := fib(a)

    write(“the fibonacci value for”, a, “ is:”, b)



    { fibonacci.o {int fib(int)} }


    Name of the object file to look for the external C function

    Signature of the C function with return types and function parameter types

    End of external C code

    Improved mechanism in detail
    Improved Mechanism in Detail

    Calling the external C functions inside Unicon

    e.g. test1.icn – Unicon program calling C functions

    procedure main()

    local i, j, str

    write("enter two variables i and j :")

    i := read()

    j := read()

    write("enter the string for palindrome check: ")

    str := read()

    write("the avg of i and j is***********: ", myaverage(i, j))

    write("the factorial of number i is****: ", factorialfunc(i))




    { fact.o { int factorialfunc (int ) },

    classavg.o { double myaverage(double, double)},

    checkpalin.o { int palindrome( char) } }


    Start of the external C function declarations

    C function signatures

    End of the external C function declarations

    Wrapper code generation
    Wrapper code generation

    Wrapper Code for the functions present classavg.o library

    #include <stdio.h>

    #include "MyIcall.h"

    double myaverage(double, double);

    int myaveragewrap(int argc, descriptor *argv)


    double returnValue;

    double arg1;

    double arg2;

    ArgReal( 1 );

    arg1 = RealVal( argv[ 1 ] );

    ArgReal( 2 );

    arg2 = RealVal( argv[ 2 ] );

    returnValue = myaverage( arg1, arg2 );

    RetReal( returnValue );


    Icon unicon stubs
    Icon/Unicon Stubs


    procedure myaverage(a[]) #calculates myaverage


    About the Shared Library -ctest1.so

    • Library contains the entries for all external C functions used inside a particular Unicon program, here it is test1.icn

    • pathload () in turn calls loadfunc() to load the external C funtion dynamically at run time

    • The stubs become written procedures of a Unicon program written for the compiler

    • Programmers’ burden is heavily reduced

    Parameter declaration for arrays
    Parameter Declaration for Arrays

    • format for declaring a function parameter to be a single dimensional array is

      • data type followed by array indices ‘[]’

      • look like: int[] or double[]

    • When array indices are found for a function parameter type

      • wrapper code for handling arrays is generated by the Unicon translator

      • support is provided for both integer and real arrays.

    Example involving arrays
    Example involving Arrays

    # test2.icn – Program using C functions having single dimensional arrays as parameters

    procedure main()

    local elements, sorted, size, loop, avg

    write("enter the size of the array: ")

    size := integer(read())

    elements := list(size, 0)

    dblelements := list(size, 0)



    bubbleSort(elements, sorted, size)

    avg := Caverage(dblelements, size)

    write("the list after getting sorted is:")

    every write(!elements)

    write("the average of the list of doubles is--> ", avg)



    { bubblesort.o { void bubbleSort(int[], int[], int) },

    arrayavg.o { double Caverage(double[], int) } }


    Calling external C functions inside Unicon

    Start of the external C function declaration

    End of the external C function declarations

    Wrapper code for arrays 1
    Wrapper code for Arrays - 1

    #bubbleSortwrap.c – Wrapper code generated for the C function bubbleSort

    #include <stdio.h>

    #include "MyIcall.h"

    int bubbleSort(int[], int);

    int bubbleSortwrap(int argc, descriptor *argv)


    int *arg1;

    int arg2;

    ArgList( 1 );

    arg1 = (int *) malloc((int) ListLen( argv[ 1 ] )* sizeof(int));

    IListVal( argv[ 1 ],arg1 );

    ArgInteger( 2 );

    arg2 = IntegerVal( argv[ 2 ] );

    bubbleSort( arg1, arg2 );

    IValList( arg1, argv[ 1 ] );

    return 0;


    Wrapper code for arrays 2
    Wrapper code for Arrays - 2

    #arrayavgwrap.c – Wrapper code for the C function Caverage

    #include <stdio.h>

    #include "MyIcall.h"

    double Caverage(double[], int);

    int Caveragewrap(int argc, descriptor *argv)


    double returnValue;

    double *arg1;

    int arg2;

    ArgList( 1 );

    arg1 = (double *) malloc((int) ListLen( argv[ 1 ] )* sizeof(double));

    RListVal( argv[ 1 ],arg1 );

    ArgInteger( 2 );

    arg2 = IntegerVal( argv[ 2 ] );

    returnValue = Caverage( arg1, arg2 );

    RetReal( returnValue );


    Macros used for wrapper code generation
    Macros Used for Wrapper Code Generation

    • Macros help in converting Unicon descriptors to equivalent C data types and vice versa

    • Basic descriptor looks as:

      • typedef long word;

      • typedef struct { word dword, vword; } descriptor;

      • dword has the information about its type

      • vword stores the actual value

    • Macros are provided are for handling Various Unicon data types: Integer, Real, Character and Arrays

      • ArgList for validating List data type

      • IListVal and RListVal: takes a Unicon list descriptor and convert them to an array of integers or reals

      • IValList and RValList: copy back the contents of C array of integers or reals into Unicon list structure


    • Unicon strings are Immutable: modifying values of the string variables when passed to C functions is not possible

    • Programmer should take care of wrapper code when using string manipulation functions inside Unicon

    • Support is provided only for Integer and Real arrays

    Future work
    Future Work

    • Making the C function calling inside Unicon into a Inline capability

    • Extending the support for C structures (struct *) and Union data types inside Unicon


    • New preprocessor directives make it easier for calling external C functions inside Unicon

    • Different data types such as Integer, Real, Character and single dimensional Array types for Integers and Reals are supported

    • New interface eliminates writing the wrapper code

    • Shared library is automatically built by the Preprocessor

    • Icon/Unicon stubs generated automatically are passed to the Unicon program